Re: [v6ops] Our IPv6-only home network and future experiments

[Brian Candler <[e-mail]>]

On 12/04/2024 16:23, Soni "They/Them" L. wrote:
>
>> 1. libc needs to decide whether to use the CLAT in preference to 
>> regular IPv4 sockets, e.g. by detecting the presence of an active 
>> IPv4 stack or default route, and/or the presence of DHCP option 108.
>
> The idea is to not have regular IPv4 sockets, it'll always use the CLAT. 

I don't think that'll work, if for example you want to move a laptop 
between a dual-stack network (which doesn't have a PLAT) and a v6-only 
network.

But consuming information from /etc and/or /run is not a big deal, as 
you say.

Maybe there is an argument for pushing this behaviour right down into 
the kernel, but libc is an easier place to experiment with it.


>>
>> Having said that, accepting incoming traffic for an application that 
>> opens an IPv4-only socket is probably not a big concern. I'd just 
>> wonder about an app that binds to 0.0.0.0 before making an outbound 
>> connection.
>
> Those are surprisingly easier to support, since they generally use a 
> random port.

True: although you don't know in advance how the socket is going to be 
used, you could allow the bind if the port is 0, and deny it if a 
non-zero port is given.

Anyway, I'm sure this will all come out in the wash, and I look forward 
to seeing your code in action. Having Linux servers be able to make 
*outbound* connections is the main thing stopping me from turning server 
networks into v6-only at the moment.

Cheers,

Brian.